The present invention is directed to a motor driven hand-held device for imparting rotary motion to a tool mounted in the device. The device includes a housing with a mass located within the housing and movable in a plane extending perpendicularly to the axis of rotation of the tool.
In hand-held devices, the reaction moment occurring at the tool during rotation must be supplied by the operator. Under normal operating conditions such a counteraction can be easily provided. As an example, however, when drilling in an inhomogeneous material, the drill can suddenly become jammed or completely blocked. Such an occurrence leads to a rapid in the required reaction moment and generally the operator is not prepared to apply such a risen moment. Under operating conditions such an occurrence may result in injury to the operator. If the operator is working on scaffolding or a ladder, there is the further danger of a loss of balance which increases the possibility of injury.
To reduce the possible exposure to accidents, it is well known to provide a clutch which reacts at a certain torque between the drive motor and the tool axis. Actuation of such a so-called overload clutch assumes, however, the application of a corresponding counter-torque by the operator. Accordingly, such a clutch affords an overload protection for the hand-held device and is only conditionally suited to protect the operator.
In another known device, a mass is located within the housing of the device and is movable in bearings in a plane extending essentially perpendicularly to the tool axis. If the device should be twisted about the axis of rotation, for any of the reasons listed above, because of its inertia, the mass is displaced relative to the housing and can operate a switch. The actuation of the switch can, for instance, be utilized to interrupt the supply of energy to the drive motor or for the operation of a disconnect clutch or a brake.
This well known arrangement, however, has several disadvantageous features. By mounting the mass in a bearing, bearing friction is developed which influences the operation of the switch. Further, oscillations can be excited in the mass, such as by vibrations, and cause a resonance resulting eventually in the actuation of the switch though there is no interference in the proper operation of the tool. The resonance of the mass can be prevented by damping, however, if an actual interruption or blockage of the operation of the tool occurs, the actuation of the switch is delayed time-wise due to the damping action.